1. Field of the Invention
The present invention relates to a glass fiber reinforced resin composition having excellent mechanical properties such as heat resistance, mechanical strength, impact strength and the like as well as excellent coatability.
2. Description of the Related Art
Glass fiber-reinforced propylene resins are put into practice in various applications such as parts of cars, electronic devices, etc. because they have excellent mechanical properties and heat resistance.
For example, it is known that resin compositions blended with crystalline polypropylene, polypropylene modified with oxygen containing unsaturated organic compound, glass fiber treated with a silane compound on its surface, and an ethylene-.alpha.-olefin rubbery polymer have excellent mechanical properties as described in Japanese Patent Publication (Kokai) No. 19347/1983.
However, polypropylene, which is one of the main components of the compositions, is nonpolar and therefore it is difficult to perform the surface treatment of the composition such as coating, printing, bonding, hot stamping, and plating by vapor deposition. Therefore various ideas have been proposed to overcome the disadvantage.
For example, it has been studied and put into practice to etch the surface of polypropylene molded products by a physical or chemical process to modify their surfaces, thus performing the surface treatment thereof. However, this process is disadvantageous in that it does not only call for complicated steps but the molded products would also cause deformation depending on of the conditions under which the etching is carried out, or the effect obtained is insufficient. Thus, the process actually gives no satisfactory results despite high costs.
On the other hand, as described in, for example, Japanese Patent Publication (Kokai) No. 76149/1975 and Japanese Patent Publication (Kokoku) No. 10265/1976, there have been proposed an improved process in which polypropylene is graft-modified with an unsaturated carboxylic acid or its anhydride such as acrylic acid and maleic anhydride in the presence of a polymerization initiator such as an organic peroxide, or a process in which such graft-modified product is blended with non-modified polypropylene.
However, these processes have defects that the amount of the unsaturated carboxylic acid or its anhydride to be introduced by graft-modification is restricted because a decomposition reaction of polypropylene with peroxide takes place simultaneously, resulting in that the effect of the modification of the surface of the resin is insufficient, or even if sufficient effect is obtained another problem on the mechanical property occurs due to the fact that the molecular weight of the resin decreases because of the decomposition reaction.